Air pollution, cigarette smoking, and the production of respiratory health.

Previous studies of the determinants of respiratory health have treated both smoking and air pollution as being exogenous. Using an instrumental variables approach, we estimate a simple production technology in which smoking is treated as being endogenously determined. Doing so, we find, increases the predicted absolute effects of smoking on respiratory health; relative to air pollution, smoking becomes a more important determinant when it is treated as an endogenous variable.